1. Field of the Invention
The present invention relates to internal combustion engines in which the crankcase is ventilated into an air supply system. The invention further relates to a method for diagnosing the ventilation system of the internal combustion engine.
2. Description of the Related Art
In internal combustion engines, a discharge of combustion waste gases can occur as a result of leakage effects at the cylinder walls of the cylinders. These combustion waste gases collect in the crankcase and as a rule are vented via an oil separator unit and a gas line, for example a hose, into the air supply system of the internal combustion engine. In order to comply with emissions limits of emissions regulations, it is necessary for the ventilation of the crankcase to be monitored as to whether a defect in the gas line between the crankcase and the oil separator unit, and between the oil separator unit and the air supply system, can reliably be detected by diagnosis.
There are various concepts for diagnosing the functionality of crankcase ventilation. On the one hand, electrical contacts can be provided on the gas lines between the crankcase and oil separator unit, and between the oil separator unit and air supply system, which contacts are opened when the gas line becomes detached or severed so that a fault can thereby be detected. Furthermore, a sealing failure in the gas lines can be detected with the boost pressure sensor by plausibilizing an air mass sensor that is disposed on the input side of the air supply system. A disadvantage here is the fact that because there are many possibilities for faults in the air supply system, an implausibility cannot be unequivocally allocated to a fault in the gas line for ventilating the crankcase.
A further possibility is to provide a differential pressure sensor between the crankcase and the environment. In the intact state, the pressure in the crankcase is lower than ambient pressure, since a pressure drop occurs in the air supply system of the internal combustion engine due to the air filter. In addition, the opening of the gas line for ventilating the crankcase generally extends transversely to the flow profile in the air supply system, so that a negative pressure occurs in the ventilation gas line because of a Venturi effect. If a fault occurs in the gas line for ventilating the crankcase, then approximately ambient pressure exists in the crankcase. With the aid of the differential pressure sensor, a pressure drop between the crankcase and the environment can be associated with a properly functioning crankcase ventilation system, and can be evaluated in a diagnostic function.
Because the pressure differences between the crankcase and ambient pressure are generally very small, implementation of the diagnostic function requires a differential pressure sensor having very small tolerances and, in some circumstances, operating points at which a high mass air flow exists in the air supply system, in order to effect a differentiation between a properly functioning and a non-functioning ventilation system.